What volume of sand would you need to make a difference? And at what rate does it collect Cs137 to reach 99%? Would it be feasible to stack filters? (E.g., 0.0

What volume of sand would you need to make a difference? And at what rate does it collect Cs137 to reach 99%? Would it be feasible to stack filters? (E.g., 0.01 * 0.01 * 0.01...)